Electrical musical instrument keying circuitry



May 24, 1966 D. M. PARK 5 Sheets-Sheet 1 Filed Dec,

A TTORNE Y May 24, 1966 D. M. PARK 3,253,077

AELECTRICAL MUSICAL INSTRUMENT KEYING CIRCUITRY Filed Deo. l2, 1963 5Sheets-Sheet 2 lINVENTOR.

BY Donold M. Pork- HM ATTORNEY.

May 24, 19.66 D. M. PARK 3,253,077

ELECTRICAL MUSICAL INSTRUMENT KEYING CIRCUITRY A TTORNE Y United StatesPatent O Electronic Development Corporation, Raleigh, N.C., a

corporation of North Carolina Filed Dec. 12, 1963, Ser. No. 330,147 12Claims. (Cl. 84-1.11)

This invention relates generally to electric musical instruments and,more particularly, to keying circuits for electric musical instruments.

Most modern electronic organs include a plurality of tone generators,usually in theform of oscillators, which are coupled to an audio systemthrough appropriate valves or gates. These valves, which are commonlyreferred to as keying circuits, are controlled by the keys of the organkeyboard so that operation of the keys determines which tones aretransmitted through the valves to the audio system. In general, it canbe said that the tone signals from the tone generators are fed into thevalves along controlling paths, and that the selected signals aretransmitted from the valves to the audio system along controlled paths.

It is the main object of the present invention to provide an improvedkeying circuit for electronic organs.

It is another object of the invention to provide an improved keyingcircuit which provides at least two controlled paths for eachcontrolling path.

It is a further object to provide such a circuit which is considerablymore economical than the keying circuits proposed heretofore.

A still further object is to provide such a circuit which converts tonesignals in the form of sawtooth or sine waves to substantially squarewaves.

Still another object is to provide such a circuit which provides tonesustaining on each controlled path.

Another object is to provide such a circuit which permits the additionof tremolo on each controlled path.

A further object is to provide such a circuit which permits the use ofvery economical oscillators.

Other aims and advantages of the invention will be apparent from thefollowing description and appended claims.

In the drawings:

FIGURE 1 is a general block diagram showing a portion of one particularelectronic organ system embodying the present invention;

FIGURE 2 is a schematic circuit diagram of one specific embodiment ofthe system of FIGURE l; and

FIGURE 3 is an illustration of the wave shapes of the tone signals atvarious points throughout the circuit of FIGURE 2.

In accordance with the present invention, there is provided an electricmusical instrument having a plurality of tone-generating oscillators; aplurality of electronic valves each of which has at least twocontrolling paths for receiving tone signals from the oscillators, andat least four voltage responsive controlled paths for selectivelytransmitting the tone signals, each controlling path being operativelyassociated with two of the controlled paths and being operativelyconnected to one of the oscillators; tone-modifying means operativelyconnected to the controlled paths and an audio system operativelyconnected to the tone-modifying means; a source of voltage for actuatingthe controlled paths; and key-operated switching means for applying thevoltage to the voltage responsive controlled paths so as to selectivelyactuate the controlled paths to transmit selected tone signals to therespective tone-modifying circuits connected to the selectively actuatedcontrolled paths.

3,253,077 Patented May 24, 1966 A preferred embodiment of the presentinvention will now be described in more detail by referring to thedrawings.

Referring first to the general block diagram in FIG- URE 1, there isillustrated a portion of an electronic organ system which generallycomprises a master tone-generating oscillator 10; three slavetone-generating oscillators 12, 14, and 16 which follow the masteroscillator 10; two electronic valve 19 and 20 which provide twocontrolled paths 21 and 22 for each controlling path 23 from thetone-generating oscillators 10, 12, 14, and 16; a keyoperated switch 24operatively connecting each of the controlled paths 21 and 22 totone-modifying circuits 25 and 26, respectively; and an audio systemcomprising an amplifier 28 and a speaker 30. Although the illustratedportion of the organ system includes only four tone-generating-oscillators and two electronic valves, it will be understood that allthese elements would be multiplied may times in the complete organsystem and, therefore, the advantages of this invention would also bemultiplied many times.

To briefly explain the operation of the system shown in FIGURE 1, themaster `oscillator 10 generates a first tone signal which is fed along afirst controlling path 23a to the first electronic valve 19. The signalfrom the master oscillator 10 is also fed into the first slaveoscillator 12, which produces a second tone signal at half the frequencyof the first tone signal. This second tone signal is fed along a secondcontrolling path 23b to the first electronic valve 19, and is also fedinto the second slave oscillator 14. -The slave oscillator'14 generatesa third tone signal at half the frequency of the second tone signal andfeeds it into the third slave oscillator 16 and also along acontr-olling path 23e to the second electronic valve 20. And, finally,the slave oscillator 16 generates a fourth tone signal at half thefrequency of the third tone signal and yfeeds it along a controllingpath 23d to the second valve '20.

The electronic valves 19 and 20 provide two controlled paths 21 and 22for each controlling path 23, and the opening of the valves to thevarious controlled paths 21 and 22 is controlled by the key-operatedswitches 24 1ocated in each of the paths 21 and 22. For example, if thekey-operated switch 24a is closed, the valve 19 opens to transmit thefirst tone signal from controlling path 23a along the controlled path21a to the tone-modifying circuit 25. Similarly, if the key-operatedswitch 24d is closed, the valve 19 opens to transmit the second tonesignal from controlling path 23b along controlled path 22h to thetone-modifying circuit 26. From the tonemodifying circuits, the signalsare transmitted on through the amplifier 28 and the speaker 30 of theaudio system.

Since the electronic valves 19 and 20 provide two controlled paths foreach controlling path, they permit two different audio effects to beobtained from each tone signal. In other words, the organ keys can beoperated to pass each of the basic tone signals through either or bothof the two tone-modifying circuits 25 and 26. Thus, although theillustrated `system produces signals of only four different frequencies,i.e. four different notes, the multiple controlled paths provided by thevalves 19 and 20 permit the production of eight different audio effects,or two different effects for each note.

One specific embodiment of the general system of FIG- UI'E 1 isillustrated in FIGURE 2. The master oscillator 10, which is aconventional transistorized Hartley oscillat-or, generates a first tonesignal at a predetermined constant frequency which represents thehighest note to be produced by the organ. For example, a suitablefrequency for this first tone signal in most organs is about 2,000cycles per second. This first tone signal, which is in the form of asine wave, is passed through a load resistor 50 into the rst electronicvalve 19, and also into the first slave tone-generating oscillator 12.

An integral part of each of the valves 19 and 20 is a triode 52 havingdual grids 55a and 55b and four plates 54, 56, 58, and 60, such as a12FQ8. The first tone signal from the oscillator is applied to the grid55a of the triode, while each of the four plates is connected to a biasvoltage -V through a load resistor 70 and a bias resistor 68. Each ofthe plate circuits of the triode 52 is also connected to atone-modifying circuit 25 or 26 through a coupling capacitor 72, and toa B+ voltage through a switch 24 wihch is manually operated by a key onthe organ keyboard.

Operatively associated with each of the key-operated lswitches 24 is atone-sustaining circuit 76 comprising a resistor 78 and a capacitor 80connected in parallel with each other. The resistor 78 of each of thecircuits 76 is connected to ground through a switch 82 which iscontrolled by a manually operated rocker arm (not shown). Thetone-sustaining circuit 76 is operative only when the switch 82 isclosed.

The tone-modifying circuits 25 and 26 may be any of the standardcircuits commonly employed in electric musical systems to modify theparticular audio effect of any given note. Typical examples of suchcircuits are the various lilters, such as iiute filters and stringfilters, and tone-selecting amplifiers.

The three slave tone-generating oscillators 1.2, 14, and 16 are allconventional relaxation oscillators composed -of a neon tu-be 84 inparallel with a capacitor 86 and connected to a voltage V through aresistor 88. The output of each of the slave oscillators is fed to agrid 55 of one of the triodes 52 through Ia resistance-capacitancenetwork comprising a capacitor 90, a resistor 91, and a resistor 92. Theoutput of the slave oscillator 12 is also fed through a coupling circuitcomposed of a capacitor 94 and a diode 95 to the slave oscillator 14which, in turn, feeds its outpu-t through a similar coupling circui-t tothe slave oscillator 16. The outputs of the slave oscillators 14 and 16are also fed to grids 55a and 55b, respectively, of the second valvecircuit 20.

OPERATION OF 'DHE SYSTEM OF FIGURE 2 In operation, the master oscillator10 generates a first constant-frequency tone signal which is applied toboth the valve 19 and thev iirst slave oscillator 12 in the form of asine wave. Each of the slave oscillators operates as a conventionalrelaxation oscillator, i.e., the capacitor 86 charges up until it firesthe neon tube, then discharges and charges up again, thereby generatinga continuous tone signal in the form of a sawtooth wave. The value ofthe capacitor 86 in each of the slave oscillators is chosen to producean output signal at exactly half the frequency of the input signal fromthe preceding oscillator. In other words, the master oscillator 10produces a first tone signal at a frequency j, the rst slave oscillator12 produces a second tone signal at a frequency f/Z, the second slaveoscillator 14 produces a third tone signal at a frequency f/4, and thethird slave oscillator 16 produces a fourth tone signal at a frequencyf/S. In each case, the

slave oscillator is locked at the desired frequency by the input signalfrom the preceding oscillator. Although any desired number ofoscillators may be employed, it will be understood that the tone signalsgenerated by the oscillators are all even multiples 'or submultiples of-each other.

As the output signal of each of the slave oscillators 12 and 14 is fedto the succeeding slave oscillator, the signal is passed through acoupling circuit composed of a capacitor 94 and a diode 95, which shapethe tone signal wave to a form suitable for locking the next oscillatorat the desired frequency. The operation of the coupling circuit can bebest explained by referring to the wave `forms shown in FIGURE 3.Referring first to the slave oscillator 12, the output signal of thisoscillator at point i A in FIGUR'E 2 appears as wave A in FIGURE 3.yWave A is a standard sawtooth wave at some predetermined positivevoltage V. As the sawtooth wave A passes through the capacitor 94, itappears as wave B at point B in FIGURE 2, which serves to lockoscillator 14 at half the frequency of oscillator 12. The output of the4oscillator 14 at point C in FIGURE 2 appears as wave C in FIGURE 3.Wave C has the same sawtooth shape as wave A, but at half the frequency.

Returning now to point A in the first oscillator 12, the

output signal at this point is passed through a Voltagedividing,wave-shaping network comprising the capacitor 90 and resistors 91 and92. The signal is first clamped, as indicated by wave D appearing atpoint D in FIG- URE 2, and then clipped, as indicated by wave Eappearing at point E in FIGURE 2. From point E, the signal is applied tothe grid 55b of the first valve 19. One important feature of thisinvention is that the output signal from the electronic valves 19 and 20are square waves, which generally produce a very desirable tone qualityin an electronic organ. waves, it is important that the capacitor 90 andthe resistors 91 and 92 be adjusted to produce a wave E which, whenapplied to the grid` 55b, causes a substantially square wave to beproduced at the plates S8 and 60. In other Words, t'he voltage appliedto the grid 55b must extend into both the saturation region and the cutoregion of the tube 5-2. The output signal of the tube 52 then appears asWave F at points F in the plate circuits.

As can be seen from the foregoing description, the various tone signalsfrom the master oscilaltor 10 and the slave oscilaltors 12, 14, and '16are applied continuously to the respective grids 55 of the tubes 52,thereby providing a controlling path for each pair of controlled pathsrepresented by the two plates associa-ted with each grid. Of course, thevarious plate circuits are normally nonconducting because of the biasvoltage -V applied across the resistors 68 and 70. But each time one ofthe manually opearted key switches 24 is closed, the particular plateassociated with that switch conducts the tone signal associated withthat plate through a coupling capacitor 72 to one of the tone-modifyingcircuits 25 or 26, and then on through the audio system. As can be seenin FIGURE 2, one of the controlled paths associated with eachc-ontrolling path leads to the tone modifying circuit 25, while theother controlled path associated with each controlling path leads to theother tone-modifying circuit 25. Thus, by selectively operating the keys24, the organ player can not only select different notes or tonesignals, but also can select different audio effects or voices for eachnote. For example, the tone signal that is fed into the valve 19 fromthe master oscillator 10 can be transmitted through eithertone-modifying circuit 25 or 26, depending on whether key 24a or 24b isdepressed, and the same is true of each of the three other tone signalsthat are fed into the valves from the three servant oscillators.

When it is desired to sustain the tone signals being conducted along anyof the controlled paths from the valves 19 and 20, the appropriateswitches 82 are closed so as to render the appropriate RCtone-sustaining circuits 76 operative. Of course, the values of theresistors 78 and the capacitors 80 in these circuits may be adjusted toprovide any desired sustaining period.

One important feature of the circuit of FIGURE 2 is that tremolo can beadded to any of the tone signals by simply modulating the B-lvoltagewhich is applied to the plates upon closing of the key-operated switches24. Thus, it is possible to add tremolo to each of the controlled paths.

Another significant feature of the circuit of this invention is that itstabilizes the tone-generating oscillators by providing a relativelyhigh load impedance, thereby permitting the use of very economicaloscillators, such as the neon-tube relaxation oscillators employed inthe circuit of FIGURE 2.

In order to obtain these square While various specific forms of thepresent invention have been illustrated and described herein in somedetail, it will be apparent that the same are susceptible of numerousmodifications within the scope of the invention. For example, althoughthe invention has been described with particular reference to a systemof tone generators comprising a master oscillator generating a sine waveand a plurality of slave oscillators generating sawtooth wave, it willbe understood that the keying circuit of the invention may be used withnumerous other tone generators producing various other wave shapes.Similarly, instead of using a master-slave tone-generating system, eachtonegenerating oscillator could be free running and precisely tuned tothe exact desired frequency. Moreover, although the electronic valve andthe controlling and controlled paths provided thereby have beendescribed with particular reference to vacuum tubes, such as the 12FQ8,it can be seen that the sa-me general circuit can be made with otheractive electronic devices, such as by the use of transistors having twobases and four collectors.

What is claimed is.

v1-. In an electric :musical instrument having a plurality oftone-generating oscillators:

(a) a plurality of electronic valves, each of which has at least twocontrolling paths and at least four voltage responsive controlled paths,each controlling path being operatively associated with two of saidcontrolled paths and being operatively connected to one of saidoscillators;

(b) a voltage source; and

(c) manually operated percussive switching means for operativelyconnecting said voltage source to selected controlled paths, therebytransmitting selected tone signals from said controlling paths throughsaid valves and along said selected controlled paths.

2. The electric musical instrument of claim 1 which includesresistance-capacitance tone-sustaining means and a second manuallyoperated switching means for operatively connecting said tone-sustainingmeans to said controlled paths.

3. The electric musical instrument of claim 1 wherein the voltage levelof said voltage source is sutiiciently high to cause said electronicvalves to conduct a tone signal from a controlling path to the selectedcontrolled path.

4. The electric musical instrument of claim 1 which includestone-modifying means operatively connected to each of said controlledpaths.

5. The electric musical instrument of claim 1 wherein a differenttone-'modifying means is operatively connected to each of the twocontrolled paths operatively associated with each controlling path.

6. An electric musical instrument comprising:

(a) a plurality of tone-generating oscillators including a masterHartley oscillator and a sequence of slave relaxation oscillatorsoperatively connected to said master oscillator;

(b) a plurality of triodes each of which has a dual grid and fourplates, each of said grids being operatively connected to one of saidtone-generating oscillators, thereby providing at least two platesoperatively associated with each oscillator;

(c) tone modifying circuits operatively connected to said plates, adierent tone-modifying circuit being operatively connected to each oftheplates associated with a single oscillator;

(d) an audio system including an amplifier and a speaker operativelyconnected to said tone-modifying circuits; and

(e) a D.C. voltage source and manually operative percussive switchingmeans for operatively connecting said voltage source t0 selected platesof said triodes, thereby transmitting selected tone signals fr0-rn saidgrids through the selected plates, through the tonernodifying circuitsoperatively connected to the selected plates, and through said audiosystem.

7. The electric musical instrument of claim 6 wherein the tone signalsapplied to said grids extend into both the saturation regions and thecutoi regions of said triodes, thereby causing a substantially squarewave to be transmitted by said triodes regardless of the wave shape ofthe signals applied to said grids.

8. The electric musical instrument of claim 6 wherein the tone signalfrom each of said oscillators is fed to said grid through aresistance-capacitance network which shapes and clamps said signal suchthat it extends into both the saturation region and the cutoi region ofsaid triode, thereby causing a substantially square wave to betransmitted through the plates of said triodes.

9. The electric musical instrument of claim 6 which includes means formodulating said D.C. voltage.

10. In an electric musical instrument having a plurality oftone-generating oscillators:

(a) a plurality of electronic valves, each of which has at least onecontrolling path for receiving tone signals from said oscillators and atleast four voltage responsive controlled paths for selectivelytransmitting said paths for selectively transmitting said tone signals,each controlling path being operatively connected to one of saidoscillators.

(b) tone-modifying circuits operatively connected to said controlledpaths and an audio system operatively connected to said tone-modifyingcircuits;

(c) a source of voltage for actuating said controlled paths; and

(d) key-operated switching means for applying said voltage to saidvoltage responsive controlled paths so as to selectively actuate saidcontrolled paths to transmit selected tone signals to the respectivetone-modifying circuits connected to the selectively actuated controlledpaths.

11. The electric musical instrument of claim 10 which includesresistance-capacitance tone-sustaining means and manually operatedswitching means for operatively connecting said tone-sustaining means tosaid controlled paths.

12. The electric musical instrument of claim 10 wherein each of saidcontrolling paths includes a resistancecapacitance network which shapesand clamps the tone signal such that said valve transmits asubstantially square wave to said controlled paths.

No references cited.

JOHN W. HUCKERT, Primary Examiner, D. D. FORRER, Assistant Examiner,

1. IN AN ELECTRIC MUSICAL INSTRUMENT HAVING A PLURALITY OFTONE-GENERATING OSCILLATORS: (A) A PLURALITY OF ELECTRONIC VALUES, EACHOF WHICH HAS AT LEAST TWO CONTROLLING PATHS AND AT LEAST FOUR VOLTAGERESPONSIVE CONTROLLED PATHS, EACH CONTROLLING PATH BEING OPERATIVELYASSOCIATED WITH TWO OF SAID CONTROLLED PATHS AND BEING OPERATIVELYCONNECTED TO ONE OF SAID OSCILLATORS; (B) A VOLTAGE SOURCE; AND (C)MANUALLY OPERATED PERCUSSIVE SWITCHING MEANS FOR OPERATIVELY CONNECTINGSAID VOLTAGE SOURCE TO SELECTED CONTROLLED PATHS, THEREBY TRANSMITTINGSELECTED TONE SIGNALS FROM SAID CONTROLLING PATHS THROUGH SAID VALVESAND ALONG SAID SELECTED CONTROLLED PATHS.